I'd be OK with Gray.
The other likely candidate is Kwame Brown, who may be a little better defensive player. Looks like Gray is a little better rebounder, but Brown is a little better defender (maybe more of a pure replacement for what we lost when we traded Perk).
I wonder if Danny will offer one of those guys a decent-sized chunk of the MLE, but for only one year.
I mean, I don't think we're realistically going to do a lot better than that, with the limited tools we have at our disposal. Starting-caliber centers usually get paid at least $8M per, and outside of trading one of the big 4 we just can't make the dollars work.
But, you could do worse than a center rotation of JO, Kwame/Gray, KG playing some smallball C, and maybe bringing back Baby Davis for year. If JO can be healthy for the playoffs (yeah, a *big* if), that'd be a pretty good defensive rotation.